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Sunday, February 17, 2013

Useful chemicals and fuel from Carbon dioxide

Carbon dioxide is abundant, non-toxic, inexpensive, and a renewable
source of carbon. This makes CO2 the most coveted compound by Green
Chemistry enthusiasts. Industries are always on the lookout for ways that will
enable effective use of CO2 to act as synthetic building blocks for
producing fuels like Methane, Di-methyl-ether and Mthanol and fine-chemicals.
Furthermore, CO2 conversion could also help reduce atmospheric CO2
levels, popularly known as “Green House Gas”, and thus, protect climate.

Nature has been highly successful in using CO2 as synthetic
building blocks in photosynthesis. For decades, scientists have been trying to understand this phenomenon at a molecular level. Such studies have proved useful in developing biomimetic catalysts for CO2 conversion. Chlorophyll (Porphyrin molecules) in green plants helps convert incident sunlight and atmospheric CO2 into sugars (energy). So, this makes them promising target for testing activation catalysts for CO2 adsorption. Effective CO2 adsorption using man-made catalysts is indeed our end-goal. Lot of research is being conducted in this area to further the economic viability of the processes that utilize CO2. Several companies are pursuing the idea / concept of thermochemical and electrochemical conversion of CO2 into chemical feedstock or polymers. Research and development are currently focused on increasing the catalyst life and bringing down the temperature of conversion.

Future research must emphasize on the rational design of highly active
catalyst, in order to satisfy the economic development of CO2
conversion. But, the development of such efficient catalysts requires
a complete understanding of CO2 and CO2-catalyst
interactions.

In order to develop such a catalyst, following points should be
considered,

CO2 has strong affinity towards nucleophiles and
electron-donating reagents, due to the electron deficiency of its
carbonyl-carbon, If the designed
catalyst has nitrogen or base-functionalty (basic), it will have an increased
affinity towards CO2 (eg, Porphyrin, Grignard reagents). Such
catalysts lead to the synthesis of acid-derivatives.

Catalyst in supercritical CO2 may also increase
stability. It is essential to make use of CO2, based on the unique
physical properties as that of the supercritical fluid, either as a solvent, or
as an anti-solvent, or reactant, or a combination of all.

Photoelectrochemistry, the study of using solar energy to
split CO2, is an emerging method for clean production of chemicals. It is also important to develop catalysts (Semiconducting
materials) for the electrochemical conversion of CO2.

Use of high-energy starting materials may ease the catalyst
role.

The catalyst will be more efficient if it has both CO2 adsorption
and activation functionality. Eg, designer MOF that contains Lewis-base sitewill donate electron to CO2, in contrast to the Lewis-acids sites in
traditional MOFs for adsorbing CO2.

Chemical reactions can also
benefit from using CO2 as a mild oxidant, or as a selective source
of O2 atoms because dissociation of CO2 on a
catalyst-surface could produce active O2 species.

The trend towards conversion of CO2 to useful chemicals and
fuels will probably intensify in the near future. This could in turn lead to
effective management to tackle climate change and energy crisis.

As George Whitesidesemphasizes, managing CO2
and conversion into useful chemicals and energy will be the reinvention of
chemistry, and it is also chemistry/ molecular solution to the important problem facing
the society. He says

“Some of the most
interesting problems in science, and many of the most important facing society,
need chemistry for their solution. Examples include: understanding life as a
network of chemical reactions; interpreting the molecular basis of disease;
global stewardship; the production, storage, and conservation of energy and
water; and the management of carbon
dioxide."

Issues pertaining to CO2 is truly global, and a major
opportunity for the development of sustainable energy options and environmental
preservation. So, use of CO2 for the synthesis of useful chemicals
& fuels will mark a new field in chemistry. It is important to establish
university-industry-collaboration to search for new-reactions &
new-catalysts in this field.

To Readers: If you have experience
with CO2 conversion reaction or specific catalyst, please feel free
to comment.

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